dendrologie

The Beltrees database – a wealth of information about trees in Belgium

Joke Ossaer1)

Summary ‒ The Beltrees database – a wealth of information about trees in Belgium ‒ The Beltrees database, created by members of the Belgian Dendrological Society, collects information on remarkable trees in Belgium and the collections in which they grow. It contains almost 30 000 records and for some entries measures have been taken repeatedly over the last thirty years. This inventory wants to contribute to the conservation and survival of remarkable trees of Belgium. It gives an indication of the richness in species and varieties planted in Belgium and of the regional distribution of certain taxa. The database puts emphasis on the value of trees, sometimes neglected by its owners or surveyors. The ranking of the trees is done according to their identity and their girth at 1.5 m above ground level.

Samenvatting ‒ De Beltrees databank – een schat aan informatie over bomen in België – De Beltrees databank, opgestart door leden van de Belgische Dendrologische Vereniging, verzamelt informatie over merkwaardige bomen in België en de parken, tuinen en andere locaties waar ze groeien. De databank bevat bijna 30 000 bomen waarvan sommige regelmatig opnieuw gemeten werden gedurende de laatste 30 jaar. Deze inventaris wil een bijdrage leveren aan het behoud en het voortbestaan van merkwaardige bomen in België. Het geeft een indicatie van de rijkdom aan soorten en variëteiten aangeplant in België en van de regionale verdeling van bepaalde taxa. De databank legt de nadruk op het waardevolle karakter van bomen, iets waar eigenaars en collectietoezichters soms aan voorbij gaan. Het klasseren van de bomen binnen hun taxon is gebaseerd op hun stam­omtrek op 1,5 m boven het maaiveld.

Sommaire ‒ La base de données Beltrees – une mine d’informations sur les arbres en Belgique – La base de données Beltrees, créée par des membres de la Société Belge de Dendro- logie, recueille des informations sur les arbres remarquables en Belgique et les collections dans lesquelles ils grandissent. Elle mentionne près de 30 000 arbres et pour certaines entrées, les mesures ont été effectuées à plusieurs reprises au cours des trente dernières années. Cet inventaire veut contribuer à la conservation et à la survie des arbres remar- quables de Belgique. Il donne une indication de la richesse des espèces et variétés plantées en Belgique et de la répartition régionale de certains taxons. La base de données met l’accent sur la valeur des arbres, parfois négligés par les propriétaires ou les responsables de collections. Le classement des arbres se fait en fonction de leur identité et de leur circonférence à 1,5 m au-dessus du niveau du sol.

1) Joke Ossaer, Arboretum Wespelaar, Grote Baan 63, 3150 Haacht (Wespelaar), Belgium. [[email protected]]

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The Belgian Dendrological Society Since 2001 the Belgian Dendrology Soci- ety has mandated the Foundation Arboretum Wespelaar to organize the management of the The Belgian Dendrological Society was Beltrees database and to assure the publica- founded in 1953 by Robert and Jelena De tion of appropriate measurements carried out Belder and Robert Lenoir amongst others. Its by many enthusiasts and volunteers. TheBel- purpose is to promote and enlarge the knowl- trees database2) can be consulted via de web- edge and cultivation of trees and shrubs. The site www.dendrologie.be and via www.arbore- Society encourages the collaboration between tumwespelaar.be (these versions are updated scientific institutions, professionals, plant lov- once a year). TheBeltrees inventory can also ers and those responsible for botanical or den- be consulted as a PDF-file on the latter web- drological collections. As a result of these site (sorted by park or sorted by name and objectives it unites amateurs and professionals circumference). The database contains almost interested in trees and shrubs. Moreover, it is 30 000 records (dead and alive), and for some the society’s ambition to actively contribute to entries measures have been taken repeatedly the adequate management and conservation over the last thirty years. of trees and shrubs, both in their natural envi- ronment as in parks and botanical collections (public as well as private). This is stimulated by The aim of Beltrees and the the organization of a variety of scientifically gathered information oriented activities (lectures, excursions and study tours abroad, publications). This inventory wants to contribute to the pub- Starting in 1985 the database has attempted lic awareness and conservation of the remark- to list all known tree collections in Belgium able and rare trees of Belgium. The aim of the (Belgard) and its remarkable and/or biggest Beltrees database is to list as much interest- trees (Beltrees). It was based initially on the ing trees in Belgium as possible. There are no work of Jean-Claude Baudouin, Michel limitations on the identity: every species or Decalut, Philippe de Spoelberch and Arthur cultivar is welcome. Over time some of the De Haeck. The data accumulated without trees will have died or been cut for whatever being really available to the public. Philippe de reason; this information is retained in the Spoelberch developed the Beltrees database database, as this may have a historical and with the help of assistants has introduced interest. all these measurements in a single database. For the most common species in the data- This made it possible to present a clear picture base, a minimum girth is required for inclu- of the situation in Belgium. In 1992 Jean- sion in the database. This minimum girth will Claude Baudouin, Philippe de Spoelberch, Jef often differ per region.Abies nordmanniana for Van Meulder and photographer Roel Jacobs, example is often measured in Wallonia published the book “Arbres de Belgique” ‒ “Bomen in België”. This book described about 2) 1 000 species and varieties found in our coun- This database is owned by the ASBL/VZW try and presented in an appendix a list of about Belgische Dendrologie Belge (respecting the rights of the individual measurers and other suppliers). It is 4 600 big or rare trees. Members of the Bel- managed by the Foundation Arboretum Wespelaar. gian Dendrology Society have continued to Usage of this data without mentioning of the source accumulate data ever since. or for commercial goals is not authorized.

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(134 times) but not that often in Flanders helps to locate specimens of rarely planted (51 times) and not at all in Brussels. That’s cultivars or species. This can be helpful to pre- why it only has a minimum girth in Wallonia, serve such cultural heritage. It also gives an which is 200 cm. Liriodendron tulipifera is indication of the regional distribution (as a measured 259 times in Wallonia, 122 times in result of climatic conditions) and use of cer- Flanders and 33 times in Brussels. The mini- tain species and of course of the diversity in mum girth therefore differs in each region: species planted in Belgium. 300 cm in Wallonia, 250 cm in Flanders and no minimum girth in Brussels. Important col- lections which are visited frequently, may list The method of ranking small but promising common trees as these may contribute to growth statistics. Only healthy trees with a single stem are The girth is measured, the height is esti- retained for the tree ranking. This ranking is mated and the location mentioned. Often a done on the base of their identity and their few specific comments about the location or girth at 1.5 m above ground level without tak- the tree are added. A tree can be remarkable ing into account the crown size, height or because of its monumentality, rareness, aes- habitus of the tree. Even a minuscule tree can thetical or historical value. be a champion if it is the biggest of a rarely planted taxon in our country. The twenty thickest trees per taxon are sub- The value of Beltrees divided into four categories. The biggest tree or champion of a specific taxon in Belgium While measuring trees in each collection, it is gets a “ ** ” symbol in the database. The next important to be able to identify the trees, ver- three are given a “ * ”, de six following a “ ° ” and ify their health status and, if possible, locate the ten following a “ . ” symbol. Dead or dying them on a map. The owner or manager of the trees are excluded from the classification. collection is provided with a copy of the meas- The ranking does not take into account the urements and sometimes also a few recom- year of measurement. Of two trees, one with mendations (e.g. suggestions about which new 355 cm circumference measured in 2012, and trees to plant or which trees to remove to cre- the other with 350 cm measured in 2005, the ate more space for the remaining trees). The first will be our champion. The tree measured database emphasizes the value of trees, some- in 2005 will probably be bigger at a specific times unknown to its owners or surveyors. time but since nobody verified this, we can’t Hopefully, once the owners are advised about take this into consideration. If for a taxon an the richness of their collection they may start identical measurement occurs, then the oldest to appreciate it and take on an active care of measurement will take priority as this speci- the collection; this should contribute to the men will most probably have the biggest cir- longevity of the trees and the collection. It cumference as of today. always helps if there is a “champion” among the trees. Such trees are always singled out and most owners will be proud and preserve these Not ranked remarkable trees special trees. The database also has a historical value. It Some interesting and big trees are excluded gives an idea of species planted in the past and from the ranking by our strict rule (a single

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stem and measurement at 1.5 m). Th ey are the graft scar (if visible) has to be mentioned nevertheless singled out as remarkable trees by in the data as well. the “-” symbol. Th ese giants usually start branching at the base or have produced mul- tiple stems. Other deformed trees may be dif- Height fi cult to measure and will also receive the “-” symbol if remarkable. Th e height of a tree has been given less impor- tance in the Beltrees database. Other coun- tries rely on the height for rankings of cham- Measuring method pion trees, but this is diffi cult to standardize and the accuracy is less sure. Girth is easy and To compare specimens correctly a consensus more factual. Further height can also fl uctuate about the measurement method is necessary. throughout a trees life: a tree may be damaged In standard situations the girth is measured at physically by storms or reduced by tree surgery. a height of 1.5 m above ground level with a Th e height of a tree is also more infl uenced by tightened tape. Th e measurement is done at a abiotic factors such as sea breeze. right angle to the axis of the stem. A leaning Of course it remains interesting to provide tree or a tree on a slope should always be a height measurement if possible. People like recorded on the average level (theoretical, his- to know where the tallest trees grow or which torical center of the stem). is the tallest of all. With the basics of trigo- If it is not possible to determine the girth nometry the height can be estimated with a at 1.5 m (for example due to the presence at simple stick. Instruments called hypsometers that height of a hump, branch, if a multi- and clinometers can record height to a greater trunked tree, etc.) the circumference is meas- degree of accuracy, however, even these can be ured at the narrowest point below 1.5 m. Th e misleading if used incorrectly or in certain cir- exact height of girth measurement and the cumstances (top of tree not visible, tree in a reason why it couldn’t be measured at 1.5 m dense forest, etc.). has to be mentioned in the data. For trees with multiple stems it can be interesting to measure the various stems on 1.5 m. Th e girth of the Identification thickest stem will be used for the ranking; the other measures may be mentioned as extra More important than girth or height is the data. When a tree was grafted, the height of correct identifi cation of the specimen. A

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measurer with good tree knowledge will notice Tree localization and recognize the most important trees in a collection at glance. Also a pocket guide or cell In order to be able to trace back a measured phone application at hand is a must. Overall tree at a later time, an exact positioning on a and detailed pictures and herbarium material map of each individual is necessary. Zoning of the specimen trees are always useful for fur- the area into numbered plots ‒ easily recog- ther confirmation of doubtful identification. nizable by natural boundary lines such as paths, ditches and land use ‒ is useful. Each specimen should be marked on a map State of health with a unique local tree number. A good start- ing point is a topographic map of the NGI The database also mentions the state of health (National Geographical Institute). For Flan- of a tree. ders and Brussels these are found via www. The codes are: geopunt.be and for Wallonia on geoportail. ɡɡ 5: plant very luxuriant, extraordinary wallonie.be. dimensions If available, GPS coordinates are added. ɡɡ 4: plant in perfect health Besides the local number (if available) each ɡɡ 3: plant not in perfect health: inadequate, tree is entered in the database with a unique weak growth, stress situation, etc. accession number, “the BDB-number”. So in ɡɡ 2: plant damaged by storm, frost or other many cases the Beltrees database indicates physical damage two numbers for each tree. Extra information ɡɡ 1: plant is dying about the location mentioned in the DATA ɡɡ 0: plant is dead (possible cause can be field often helps to find back the right tree on mentioned) site (e.g.: “along wall, group of 3: easternmost The database counts 28 097 living trees tree measured”). (December 2015). An overview per state of health is given in Table 1:

Table 1. Overview of living trees Analysis of the taxa in the Beltrees database per state of health. Table 2 lists the most frequently measured % of living State Quantity trees trees in Belgium. There are 31 taxa for which 5 691 2.5 more than 200 trees are measured, with Fagus sylvatica f. purpurea [Ill. 1] being the most 4 24 811 88.3 popular (1 082 specimens), followed by Quercus 3 1 663 5.9 robur (859). 2 694 2.5 The database contains 1 859 different living 1 238 0.8 taxa. Half of these are botanical species and half are hybrids or cultivars. About 800 taxa The database contains 1 712 dead trees are represented by only one specimen! These (5.7 %) which were cut or died of illness or age are rare and seldom planted species or culti- since the start of the measurements. Many vars. Collections with a lot of trees could check large and high trees have disappeared follow- if they have some extra trees of those 800 sin- ing bad gales. gle member taxa in their possession.

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Table 2. List of most frequently measured trees in Belgium (girth >2 m) with number of specimens per taxon. Name Quantity Name Quantity Fagus sylvatica f. purpurea 1 082 Fagus sylvatica ‘Pendula’ 312 Quercus robur 859 Taxus baccata 304 Aesculus hippocastanum 748 Acer platanoides 303 Platanus ×hispanica 727 Tilia ‘Petiolaris’ 292 Fagus sylvatica 689 Ginkgo biloba 281 Castanea sativa 579 Acer pseudoplatanus ‘Leopoldii’ 274 Sequoiadendron giganteum 515 Tilia cordata 265 Tilia platyphyllos 464 Juglans nigra 255 Fraxinus excelsior 454 Acer saccharinum 251 Liriodendron tulipifera 399 Cedrus atlantica ‘Glauca’ 250 Quercus rubra 388 Robinia pseudoacacia 248 Taxodium distichum 369 Juglans regia 242 Tilia tomentosa 358 Pseudotsuga menziesii 219 Carpinus betulus 349 Picea abies 209 Tilia ×europaea 337 Salix alba 202 Acer pseudoplatanus 316

1 – Fagus sylvatica f. purpurea (BDB 959). Outstanding specimen (840cm at 1m). Chateau de Beloeil [R. Jacobs, 4-05-2009]

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About 90 taxa have disappeared from the for our climate. And some are just annoying Beltrees database since the beginning of the and difficult like Acer caudatum subsp. ukurun- measurements in 1985. This means that the duense which is a suckering plant. But some measured trees of these taxa are dead but there taxa are interesting to access again if possible still can exist not yet measured trees of these (e.g. Magnolia acuminata var. subcordata, taxa in other collections. After cleaning this Catalpa fargesii f. duclouxii, Quercus gambelii, list (synonyms, taxa with uncertainties about Sorbus mougeotii). the identity and taxa with unresolved names) 66 missing taxa remain. They are listed in Table 3. Some of them are not very interesting Analysis of the girth (questionable cultivars as Acer saccharinum ‘Wagneri’) obscure or not even trees (e.g. Dis- Table 4 gives an overview of the amount of anthus cercidifolius). Others like Cornus capi- inventoried trees sorted by girth and by tata and Drimys winteri are not hardy enough category.

Table 3. List of taxa disappeared in Beltrees. Acer caudatum subsp. ukurunduense Cupressus macrocarpa Prunus grayana Acer ×freemanii ‘Elegant’ Disanthus cercidifolius Prunus mume Acer caesium subsp. giraldii Drimys winteri Quercus gambelii Acer pseudoplatanus ‘Tricolor’ Eucalyptus pauciflorasubsp. niphophila Quercus petraea ‘Cochleata’ Acer saccharinum ‘Wagneri’ Gleditsia japonica Quercus robur ‘Purpurascens’ Alnus incana ‘Laciniata’ Ilex ×altaclerensis ‘Camelliifolia’ Quercus robur f. variegata ‘Fürst Schwarzenburg’ Alnus maritima Ilex ×koehneana Rhamnus cathartica ×Amelasorbus jackii Larix kaempferi ‘Pendula’ Salix arbutifolia Aralia spinosa Ligustrum ovalifolium Salix magnifica Betula corylifolia Magnolia acuminata var. subcordata Sorbus americana ‘Belmonte’ Betula ermanii ‘Grayswood Hill’ Magnolia sinensis Sorbus aria ‘Gigantea’ Betula utilis var. jacquemontii ‘Silver Magnolia ×thompsoniana ‘Olmen- Sorbus aucuparia ‘Fastigiata’ Shadow’ hof ’ Caragana arborescens Malus kansuensis var. calva Sorbus cashmiriana Carpinus betulus ‘Variegata’ Picea abies Columnaris Group Sorbus mougeotii Catalpa bungei Picea brachytyla var. rhombisquamea Sorbus vilmorinii Catalpa fargesii f. duclouxii Pinus aristata Stewartia sinensis Celtis occidentalis var. pumila Pinus cembra ‘Compacta Glauca’ Thuja occidentalis ‘Gracilis’ Cercis canadensis var. texensis Pinus flexilis var. reflexa Thuja occidentalis ‘Wareana Lute- scens’ Chamaecyparis obtusa ‘Ericoides’ Pinus parviflora ‘Blue Giant’ Ulmus crassifolia Chamaecyparis thyoides ‘Andelyensis’ Populus ×canadensis ‘Raverdeau’ Ulmus glabra ‘Lutescens’ Cornus capitata Populus ×canescens ‘Macrophylla’ Ulmus minor ‘Louis Van Houtte’ Cupressus bakeri Prinsepia sinensis Ulmus procera ‘Argenteovariegata’

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Table 4. Inventoried trees sorted by girth and by category. Quantities per champion category Girth Total quantity ** * ° . - other > 7 m 81 13 19 9 6 25 9 6-7 m 235 13 23 46 42 21 90 5-6 m 1 004 25 45 63 86 93 692 4-5 m 3 004 69 108 133 126 214 2 354 3-4 m 6 056 112 217 276 384 249 4 818 2-3 m 7 558 175 363 472 539 252 5 757 1-2 m 6 409 298 600 622 630 178 4 081 < 1 m 3 467 250 708 562 365 62 1 520 Total 28 097 960 2 089 2 196 2 185 1 105 19 562

Table 5. Most frequently measured trees There are 316 trees with a girth of more with girth >6 m. than 6 m. They belong to a limited quantity of Number taxa with Sequoiadendron giganteum unsurpris- Name per taxon ingly as the most frequent (74 specimens > Sequoiadendron giganteum 74 6 m) followed by Fagus sylvatica f. purpurea: Fagus sylvatica f. purpurea 37 see Table 5. Castanea sativa 28 From the trees listed in Table 5, 81 trees Quercus robur 27 measure more than 7 m and 22 trees even Tilia platyphyllos 26 more than 8 m. Those are listed in Table 6. Platanus ×hispanica 23 On analysing Table 6 one will notice dif- Fagus sylvatica 19 ferences in the measuring dates of these trees. Salix alba 11 As a consequence the real actual sequence of Cedrus libani 9 some trees in this list can be different. This is Tilia ×europaea 9 an inherent disadvantage of the ranking meth- Tilia cordata 8 odology, but it can be a motivation to locate Platanus orientalis 6 and revisit the trees which have measurements Liriodendron tulipifera 5 dating back to previous century. Populus ×canadensis 5 Surprisingly, the thickest tree in this list Fraxinus excelsior 3 isn’t a champion. The data mentions an old Acer pseudoplatanus, Carpinus betulus, 2 fused hedge base, measured at the base but Populus ×canadensis ‘Marilandica’, Tax- very beautiful. So it is listed as a remarkable odium distichum, Tilia tomentosa tree and can’t join the ranking since it does not Acer pseudoplatanus f. purpureum, Aescu- 1 have a single stem and couldn’t be measured lus hippocastanum, Ailanthus altissima, at 1.5 m. The latter is the case for most of the Catalpa bignonioides, Cedrus atlantica, Fraxinus excelsior ‘Pendula’, Ginkgo trees in this list mentioned as remarkable or biloba, Pinus nigra subsp. nigra, Ptero- without rank symbol. carya fraxinifolia, Quercus petraea, Quer- Over the years a few of those biggest cus ×rosacea, Quercus rubra, Salix ×rubens, trees were measured several times. Table 7 Taxodium distichum ‘Pendens’, Thuja gives an overview of their average yearly plicata, Ulmus procera growth rates:

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Table 6. Thickest trees (>8 m girth). Year Girth (cm) Name + BDB number Rank last Location @ 1.5 m measure Fagus sylvatica (BDB 28293) - 1 200, (@base) 1999 Stoumont, Liège Quercus robur (BDB 326) [Ill. 2] ** 995, 2006 Eghezee (Liernu), Namur Fraxinus excelsior ‘Pendula’ (BDB - 980, 1994 Chateau de la Catoire, Leuze-en- 27467) Hainaut (Blicquy), Hainaut

Platanus ×hispanica (BDB 2060) - 940, (@0.5m) 1987 Chateau du Saulchoy, Soignies, Hainaut Platanus ×hispanica (BDB 13138) - 923, (@1m) 2008 Gemeentepark De Kwabeek, ­Boutersem, Vlaams-Brabant

Sequoiadendron giganteum (BDB ** 922, 2013 Domaine du Rond-Chêne, Esneux, 2092) [Ill. 3] Liège Castanea sativa (BDB 8383) ** 919, 2014 Schoubroek Kasteel, Lovendegem (Vinderhoute), Oost-Vlaanderen Tilia platyphyllos (BDB 7766) - 918, (@base) 2004 Vordenstein, Schoten, Antwerpen Cedrus libani (BDB 7595) 909, (@base) 2004 Ommerstein, Dilsen (Rotem), Limburg Platanus ×hispanica (BDB 963) 903, (@0.7m) 2007 Chateau de Beloeil, Beloeil, ­Hainaut Castanea sativa (BDB 28769) 900, (@base) 1995 Chateau de Franc Waret, Fernel- mont (Franc-Waret), Namur Taxodium distichum (BDB 2419) ** 897, 2012 Chateau de Marchienne, Mons (Harveng), Hainaut Tilia platyphyllos (BDB 726) ** 885, 2007 Ciney (Conneux), Namur Platanus orientalis (BDB 4324) - 860, (@0.5m) 2001 Chateau d’Agbiermont, Beauve- chain (Nodebais), Brabant Wallon Populus ×canadensis ‘Marilandica’ - 850, 1989 Geraardsbergen, Oost-Vlaanderen (BDB 4917) Fagus sylvatica f. purpurea - 840, (@1m) 2015 Chateau de Beloeil, Beloeil, (BDB 959) ­Hainaut Fagus sylvatica (BDB 5630) ** 837, 1996 Houffalize (Mabompre), Luxem- bourg Quercus robur (BDB 28464) - 825, (@base) 1997 Bastogne (Noville), Luxembourg Tilia cordata (BDB 21809) - 820, 1997 Nannut (Petit-Hallet), Liège Quercus ×rosacea (BDB 28974) - 815, 1992 Viroinval (Olloy-sur-Viroin), Namur Sequoiadendron giganteum * 814, 2006 Arboretum Louis Empain, Esneux, (BDB 2138) Liège Fagus sylvatica (BDB 4354) 810, (@base) 1989 Closerie du Rond-Chêne, Esneux, Liège

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2 – Quercus robur (BDB 326). Champion tree 3 – Sequoiadendron giganteum (BDB 2092). Champion (995cm in 2006) Eghezee (Liernu) tree (922cm in 2013). Domaine du Rond-Chêne, [R. Jacobs, 22-11-2011] Esneux [R. Jacobs, 1-09-2013]

Table 7. Overview average growth rates Liernu “Gros Chêne de Liernu”, a tree of of some of the biggest trees in Beltrees. about 700 years old according to the literature Growth (some even say 1000 years but that is surely an Name + BDB number rate exaggeration). The tree is completely hollow so (cm/year) no measurement of growth rings is possible. Taxodium distichum (BDB 2419) 6.20 Until the 1980’s, it still had a growth rate of Sequoiadendron giganteum (BDB 2092) 5.83 2 cm/year; but the tree has clearly been declin- Cedrus libani (BDB 7595) 4.43 ing the last years. It should be noted however Tilia platyphyllos (BDB 726) 3.44 that thanks to the large number of measure- Fagus sylvatica f. purpurea (BDB 959) 3.41 ments in the Beltrees database, it is possible Castanea sativa (BDB 8383) 2.96 to calculate an average and trustworthy growth Quercus robur (BDB 326) 0.60 rate per taxon. This could be the subject for a next article. Obviously one cannot use these figures as general average growth rate for the species, but this gives an indication of the differences in Measurements per region growth rate according to the species. Quercus robur (BDB 326) with its growth rate of About 50 % of the trees listed in Beltrees 0.6 cm/year is clearly not average for the spe- grow in Wallonia which is less than you would cies. It refers to our thickest champion tree in expect by its total surface (55 % of Belgium)

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Table 8. Measurements per region. Quantity Quantity Area per region Region % % % of trees of collections (km²) Flanders 10 905 38.8 379 33.4 13 522 44.3 Wallonia 14 114 50.2 622 54.9 16 844 55.2 Brussels 3 078 11.0 132 11.7 162 0.5 Total 28 097 1 133 30 528

and the important forested areas in the south D5: highest score: needs at least two points of the country. The Brussels region counts for out of 3: 11 % of all measures although it only counts ɡɡ ≥75 entries for 0.5 % of the surface of Belgium. ɡɡ ≥ 5 champion trees (**)3) or 2 of * This is explained by the high density of ɡɡ ≥ 40 special trees (**,*, °, ., -) collections in this region (0.8 collections per D4: needs at least two points out of 3 or km²) compared to Flanders (0.3) and Wal- one point from D5: lonia (0.35) and because its collections belong ɡɡ ≥40 entries to the most inventoried in the context of ɡɡ >1 champion trees (**) or 2 of * Beltrees. ɡɡ ≥ 15 special trees (**,*, °, ., -) D3: needs at least two points out of 3 or one point from D4: The database Belgard ɡɡ ≥20 entries ɡɡ 1 champion tree (**) or 2 of * TheBelgard database is a part of Beltrees. ɡɡ ≥5 special trees (**,*, °, ., -) It is the list of all participating collections (all D2: >at least one special trees (**,*, °, ., -) parks, gardens, estates,… where trees have D1: no special trees (**,*, °, ., -) been measured). It contains all possible rele- D4 and D5 are the collections which would vant information about each collection (code, be recommended to foreign visitors (compa- address, owner and/or person in charge, public rable with the Michelin stars: merits a trip, or private, surface, accessible or not or only by deserves a detour). appointment…). It may also list such infor- This ranking was revised by a team of mation as the date of foundation, historical experts, tree measurers and members of the and aesthetic value. Every important park or BDB board by region (Flanders, Brussels and collection has received a unique 5 lettered Wallonia). In this evaluation extra criteria code. Two extra codes are used: the code such as collection diversity, historical aspects, “ISOLE” for trees not located in a specific clear and correct labeling or young plantations park and the code “VARIA” for smaller parks of future interest (not yet in Beltrees) were without their own code. In this case the taken into account which could overrule the address is given in the data field. The database theoretical ranking. This exercise was a good lists 1 130 important collections. base to determine the priority collections to The collections are also ranked by dendro- logical value. To formalize the ranking of the 3) (**) the biggest of a specific taxon, (*) the 3 next, parks in Belgard a number of quantifiable (°) the 6 following, (.) the 10 following, (-) remarkable guidelines were developed: or well-known but not running in the ranking

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revisit (to update the Beltrees data). Some Some unrated collections may have many parks have been visited many years ago and interesting young plants but no measurements. possibly not very thoroughly. For those the The ranking isn’t static or an indisputable fact. actual ranking might be unsatisfactory. There- It only gives a first indication about the den- fore, it is important to take the date of the last drological quality of the collection. This is measurement into consideration. Often out- work in progress. dated inventories are incomplete. In order to Collections with a D5 rank at the moment actualize the database, the collections to be are listed in Table 10. revisited have been identified and assigned to The desire for a higher rating can be a stim- the various teams of measurers in each region. ulus for collection holders to carry out addi- Again, it is hoped that following these updated tional plantings in order to rejuvenate the col- measurements, the owners will be encouraged lection, to ameliorate the labeling system and to give extra care to their collection. to provide space to champion trees by cutting At the moment 1 110 of the 1 130 collec- less valuable trees in the immediate vicinity. tions in Belgard have been evaluated and received a dendrological rating. The quantity per rating is listed in Table 9: Conclusion

Table 9. Quantity of collections TheBeltrees database gathers a lot of inter- per rating and per region. esting and valuable data about remarkable trees in Belgium and the collections in which they grow. The aim is to contribute to the pub- lic awareness and conservation of the remark- Ranking Brussels Flanders Wallonia Quantity able and rare trees of Belgium. The database D5 28 3 13 12 also has a historical value. It gives an idea of D4 51 4 23 24 species planted in the past and of the regional D3 210 24 89 97 distribution in Belgium. The ranking of the D2 615 50 193 372 collections gives an impression about the den- D1 206 49 47 110 drological value of those collections. Hope- unranked 20 3 9 8 fully it can be a stimulus to visit them more Total 1130 133 374 623 often and keep them safe and sound for the next generations. The Beltrees database is a Of the 1 130 collections in Belgard 55 % never ending team work which considers a lot are found in Wallonia, 33 % are in Flanders of enthusiastic people spending a lot of time and about 12 % are in Brussels. Immediately measuring and remeasuring trees. But by noticeable is the big quantity of D2 and D1 measuring trees we keep an eye on them, see collections in Wallonia compared to Flanders. how they evolve, learn more about their dif- It seems measurers in Wallonia took more ferences and peculiarities and appreciate their effort in measuring small collections in the existence even more. So if you feel an urge to past. Especially via “Région Wallonne”, the go and measure trees, join the Beltrees Wallonian governement a lot of trees have measurers. Your work will be very much been measured. appreciated.

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Table 10. Collections with rank D5 in 2015. Name City PR Arboretum de Bertrix Bertrix LX Arboretum van Bokrijk Genk LM Arboretum de la Citadelle Namur NM Arboretum Groenendaal Hoeilaart VB Arboretum Kalmthout Kalmthout AN Arboretum Het Leen Eeklo OV Arboretum Robert Lenoir Rendeux LX Arboretum Saint Michel Saint-Hubert LX Arboretum van Tervuren Tervuren VB Arboretum de la Tessenire, Promenade Delsaux Esneux LG Arboretum Wespelaar Haacht (Wespelaar) VB Bois-Saint-Jean (Sambree) La-Roche-en-Ardenne LX Botanische tuin, Universiteit Gent Gent OV Chateau de Reux Ciney (Conneux) NM Closerie du Rond Chêne Esneux LG Domaine de Mariemont Morlanwelz HN Esneux Esneux LG Hemelrijk Essen AN Herkenrode Haacht (Wespelaar) VB Hof ter Saksen Beveren OV Huizingen Provinciaal Domein Beersel (Huizingen) VB Jardin Botanique de Bruxelles St-Josse / St-Joost-ten-Node BR Jardin Botanique de Liège Liège LG Kapelleberg Herent (Winksele) VB Parc de Woluwe / Park van Woluwe St-Pieters-Woluwe / Woluwe St-Pièrre BR Parc Tenbosch / Park Tenbos Ixelles / Elsene BR Pinetum Anthoine Ham-sur-Heure-Nalinnes ( Jamioulx) HN Plantentuin Meise Meise VB Provinciaal Domein Rivierenhof Antwerpen (Deurne) AN Royal Golf Club du Ravenstein Tervuren VB

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